Wednesday, March 25, 2015

As I move through my training and think ahead to my future career, I wonder: who will pay for all this research I want to do on dogs? I have so many questions to ask!

What changes happen in the canine brain as it enters, and then leaves, the socialization period?

How is the brain of a fearful dog different from that of a confident dog?

What are the genetic differences behind these variations?

How do environmental differences (prenatal stress, early learning, adult life) change the brain?

In other words, what are the mechanisms in the brain that differ in fearful dogs — receptors, neurotransmitters, synaptic wiring? And how can I learn about them without using invasive (painful and/or terminal) techniques?

Who are the caretakers of Dog, the species, who care about fearfulness? We as dog owners and lovers care, but dog owners and lovers aren’t the ones who are trained to heal unhealthy dogs, to perform research aimed at understanding them, and we (mostly) aren’t the ones who breed them. So who are the groups who are the caretakers of Dog, and what subsets of Dog do they care for?

Veterinarians

We (I am a veterinarian) are trained to heal sick dogs. Relatively few veterinarians perform research compared to those who engage solely in clinical practice. But some do perform research: most commonly as faculty at veterinary schools alongside a clinical practice, or less commonly as researchers without a clinical practice at research instititutions.

Veterinary research, as a result of this strong emphasis on healing the unhealthy, is focused on clinical results. Veterinarians most commonly perform research which asks questions about the effectiveness of particular techniques — medications, surgical approaches, new equipment. Veterinary research very rarely addresses root questions about mechanisms, particularly in the area of behavior. Rather than asking “How are the brains of fearful dogs different?”, veterinary research is more likely to ask how we could fix a fearful dog: “Does this medication make a fearful dog less fearful?”

In fact, as I pursue my mechanism-based questions, I am asked if I miss being a veterinarian. The perception is that because I am engaged in basic, rather than clinical, research, I am no longer working as a veterinarian.

Basic science researchers

If veterinarians do clinical research studies, then who does basic research biomedical studies, studies that look not at how to fix problems but at how the body works? Ph.D. researchers are more likely to do this sort of research, which is why I am currently engaged in obtaining a Ph.D.

Traditionally, Ph.D. researchers have not been interested in dogs. In fact, way back in 2004 when I was originally deciding between a Ph.D. and a D.V.M., I was told by a Ph.D. animal behaviorist, “Ph.D.s don’t study domesticated animals. Veterinarians study those.” (Actually, veterinarians mostly just try to fix unhealthy domesticated animals, not study the healthy ones.)

That perception has changed in a big way in the intervening eleven years. There are now multiple laboratories studying dogs. But where does their funding come from — who cares enough about dogs as dogs, not as models for human problems, to provide the impressive funding needed for a genomics study? (The work I am doing for my Ph.D., sequencing messenger RNA, costs around $45,000.)

The U.S. federal government

The traditional source of funding for basic research is the federal government: the National Institutes of Health for health-based research and the National Science Foundation for more basic research. But these two massive institutions are very much focused on human health — as they should be, as they are funded by the tax dollars of American citizens. The economy can’t support all the research American researchers would like to do, and getting an NIH or NSF grant is becoming more and more difficult as grant funding is cut. Funding to study dogs as models of human disease? Maybe, but isn’t it easier to study laboratory rodents (on which you can perform invasive studies) or work on humans directly? Funding to study dogs as dogs? Go lie down until it passes.

In my experience, the small number of laboratories directly studying dogs are either studying them as models for questions about human health or evolution, operate on a shoestring budget, or have great trouble obtaining funding for what they want to do.

I reviewed some of the research these two organizations have performed on how to identify and treat food aggression in shelter dogs in my story for the Bark on shelter behavioral assessments. This was ground-breaking research and I am really glad to see it published. But it doesn’t ask the basic (i.e., non-applied) research questions I am interested in: what is it about the brains of these dogs that differs from the brains of dogs without food aggression? That kind of research doesn’t have immediate applied benefit. You can’t take it to a shelter worker with a recommendation about whether or not to put a food aggressive dog on the adoption floor. It is incredibly impressive that these shelter-focused organizations perform any research at all, and it is absolutely appropriate that the research they perform should have a highly applied focus, with clear questions that, when answered, will provide guidance on how to improve the lives of shelter dogs, immediately. They do not have the resources to pursue these sort of mechanism questions that I want to ask, which do not have immediate applicability.

So who cares about understanding how dog brains work, with the hope that that information will provide a base for future applied research? Who cares about the whole species, not just the subset in shelters or the subset in hospitals?

These organizations can fund basic research on how and why particular diseases occur in their breeds, and may even be willing to fund expensive genetic studies, such as a recent one on the genetics of cancer in Golden Retrievers, supported in part by both the AKC/CHF and the Golden Retriever Foundation. However, their focus is very much on the problems of a particular breed. My questions are broader: why do dogs of all breeds have different personalities, some more or less fearful? These organizations are really the caretakers of breed subsets of Dog, not of Dog itself.

Who, then?

Who does that leave as a group willing to fund studies on Dog? On problems common to all breeds? On problems which may or may not provide good models for humans? If I hope to one day run a laboratory which studies these problems, who can I hope to help pay for the research?

I would be remiss if I did not mention Morris Animal Foundation here. While their important Golden Retriever Lifetime Study happens to focus on the health issues of a single breed, their mission is to fund research into studies of small animals (dogs and cats), livestock, and wild animals, with no breed limitations. This group is doing important work, and I applaud them.

But one organization is not enough for a laboratory to depend on for survival, especially in these times with research funding so hard to come by. And so I wonder: are we, the dog lovers of the world, the ones to start supporting research into what it is to be a dog? We, who own dogs of all breeds and mixes, with all sorts of problems, who know what problems most plague us as owners — not just medical problems, but behavioral ones?

And so I leave you with my dreams of crowdfunding, in which a researcher proposes a study and asks the public to support it through donations. Such an approach allows the dog community to take the task of answering basic questions about Dogness into their own hands. This direct connection between a researcher and the community affected by their research is a new benefit of this age of social media. Is this approach right for this particular problem? Time will tell.

Monday, March 9, 2015

A dog on leash, seeing another dog, explodes into a fury of barking and lunging. Reactive dogs, dogs who respond with arousal or aggression to what should be innocuous stimuli, can be very difficult for their owners to manage safely. I've written previously about hormonal changes in individuals experiencing this kind of arousal. But why do their brains trigger the stress response in such inappropriate situations in the first place?

Learning and memory

Past learning, stored as memories, has a lot to do with current behavior. If a dog has made bad associations with something in the past, he has a good chance of expecting a similarly unpleasant experience the next time he encounters it or something that reminds him of it. How he chooses to deal with this situation — aggression or withdrawal — is one interesting question, but right now I’m writing about how he makes associations in the first place and how he retrieves them later.

Learning and memory can mean a lot of different things depending on their context. I’ll be using them in a very narrow sense.

Learning: making an association between a stimulus and a consequence

Memory: the ability to retrieve a previously-formed association

So if a puppy is attacked by another dog, he may learn to associate other dogs with pain and fear. When he later encounters another dog, he uses his memory to retrieve that association. Two parts of the brain which are deeply associated with this type of learning and memory are the amygdala and the hippocampus.

The amygdala is associated with threat evaluation: is that twisty shape I see out of the corner of my eye a stick, or a poisonous snake? Is the dog I am greeting friendly, or about to attack me? People with damage to their amygdalas may have difficulty evaluating threats, to the extent that they may not be able to feel fear. As a result, the amygdala functions in emotional learning: people told scary stories remember them better than less exciting stories partly because of the emotional contributions of their amygdala, which tells them that an experience has some level of threat and should be recorded in memory with particular care.

The hippocampus, on the other hand, is famous for its contributions to learning different locations. London cab drivers must spend years memorizing the twisty street map of their city, and when they are done, their hippocampuses are actually larger in size compared to people who haven’t gone through the training.

When they work well, these two brain structures are an
important part of the process of identifying appropriate threats and
discarding stimuli that aren’t threatening, based on previous
experience. So what exactly is going on when they operate as they should?

Fear conditioning: contexts and cues

The most effective studies that have been done to determine exactly how the hippocampus and amygdala function in learning and memory have used fear conditioning, often in laboratory rodents. Dog trainers use classical conditioning to associate stimuli that a dog considers threatening with something positive, to change the dog’s emotional response to that stimulus — for example, to teach a dog who fears other dogs that they will reliably get food when other dogs approach, so that the dog comes to look forward to the approach of another dog as a chance to get a treat. Fear conditioning researchers do the opposite, teaching a laboratory rat that something previously benign (like the sound of a bell) predicts something aversive (like an electric shock).

It’s unfortunate that so much research has been done on how to teach fear, something we don’t actually want to do in real life. However, what we learned from these studies should translate to the types of classical conditioning we do with dogs, and be even more relevant to helping us understand how fear-based behavior issues come about in the first place.

These studies have shown that that contexts and cues are important in classical conditioning. If you put a rat into a blue cage and then repeatedly play a bell right before shocking him, he will learn to fear the sound of the bell. The blue cage is the context; the bell is the cue. If you move the rat into a purple cage and play the tone without a subsequent shock, the rat will learn that the purple cage represents a different context, and that he does not need to fear the cue in that context. So the cue and the context contribute differently to classical conditioning.

Source: Nature Reviews Neuroscience 14, 417–428 (2013)

In the case of a reactive dog, we might imagine that this dog spent time in a rough playgroup as a puppy, and learned to associate other dogs with being bullied. Here, the cue is another dog, and the context is the room the playgroup was in.

The hippocampus: learning in context

One of the jobs of the hippocampus is to encode contexts. Those London cab drivers with oversized hippocampuses have countless contexts encoded to represent many different locations around London. The hippocampus of the puppy who had a tough time at playgroup encoded the room where playgroup happened as a context.

In the case of our laboratory rats, the hippocampus encodes the blue cage as one context and the purple cage as another. With a healthy hippocampus, the rat can differentiate between the two contexts, and is fearful of the cue only in the appropriate context. But with a damaged hippocampus, the rat can’t differentiate between the blue and the purple cage. Although he was trained that the bell only predicts a shock in the blue cage, he fears both cages, because his hippocampus is unable to properly represent the context of the blue cage.

The associative amygdala

One of the jobs of the amygdala, on the other hand, is to encode associations. It encodes the association between cue and stimulus (bell predicts shock) and between context and stimulus (the shock only happens in the context of the blue cage). When humans were tested with functional MRI to see which regions of their brain became more active during a fear conditioning trial, the amygdala and hippocampus responded in different situations. When humans were trained to associate a cue with a shock, their amygdala activated in response to the cue. When they were trained to associate only a context with a shock, both their amygdala and their hippocampus activated when they were exposed to that context. The amygdala activated in both cases because the association was being recalled in both cases, but the hippocampus was only activated when the particular context was recalled. Fascinatingly, this study also found that humans with larger hippocampus volume had greater fear responses in fear conditioning trials. There was no association between amygdala size and fear response.

Prefrontal cortex as mediator

We are not, thankfully, completely at the mercy of the whims of our hippocampus and amygdala, subject to uncontrollable fears based on past bad experiences. We have some ability to take a step back and calm ourselves down. One of the parts of the brain involved in this higher-order cognition is the prefrontal cortex (PFC). This region of the brain has direct connections to both the hippocampus and the amygdala and appears able to mediate some of the signals coming from those two regions. Functional MRI studies tell us that while fear acquisition involves the amygdala, fear extinction (learning to let go of a fear) involves the PFC as well. We also know that people who have thicker PFCs are better at extinguishing fear associations. This mediation by the PFC is what lets us take a deep breath and choose not to give in to our fears.

Do dogs have this ability to take a step back and try consciously to decrease their fears? Certainly they are not as good at this skill as humans are, but I wonder if they do have some ability to do this. In a recent post at Reactive Champion, a reactive dog owner describes a situation in which she believes her reactive dog did just that.

PTSD: failure to contextualize?

When this system goes wrong, how does it go wrong? One hypothesis suggests that post-traumatic stress disorder (PTSD) is a disease of failure to contextualize. Humans with PTSD report having flashbacks to previous trauma unexpectedly and uncontrollably, and in inappropriate contexts. If you were in a drugstore during a robbery, it would be appropriate for you to remember that traumatic event when you returned to that location, and even to feel trepidation about entering that store again. You’d probably think about the event a lot for the first days, weeks, perhaps months afterwards, in many other contexts, as well. But your brain should recover, and you should eventually come to not think of it constantly, and only be reminded of it in similar contexts, such as the same or similar locations.

People with PTSD, however, may have trouble limiting their recall of traumatic events to similar contexts, so that they may be retrieving these memories (often vividly) in any and all contexts, years after the trauma has passed. The problem may lie with their hippocampus, which may have difficulty limiting recall by context. And indeed, studies have shown that people with PTSD often have smaller sized hippocampuses compared to the healthy population.

The perspective of the reactive dog

On to the realm of pure speculation, then, because studies haven’t been done in hippocampus function in reactive dogs. But I think the story of the person involved in a trauma who can’t appropriately contextualize her memories is similar to the story of the dog who was involved in a trauma (dog attack, overwhelming experience in a crowded area as a puppy) and can’t contextualize the experience. A dog who is attacked by other dogs at a dog park may learn to fear the dog park, but if never attacked outside of the dog park, should he learn to fear all dogs, everywhere? I’d argue that that’s an inappropriate association for his brain to make, and that the mechanism of failure might have to do with a failure of the hippocampus to appropriately contextualize, just as in someone with PTSD.

I’m certainly not saying that all reactive dogs have PTSD, but I am speculating that the mechanisms might be similar. Does hippocampal function vary across a spectrum, with some individuals having high-functioning hippocampuses and others not so effective ones? Do dogs with hippocampuses on one end of that spectrum have difficulty limiting their negative associations, such that they are more likely to suffer from fearfulness and possibly fear aggression? I don’t know, and I don’t know if the research will ever be done, but it’s an intriguing story to consider.

Tuesday, March 3, 2015

[Note: this infographic is intended for use in my online class, The Canine Brain: From Neurons to Behavior, which starts tomorrow (March 3, 2015). Check it out if dog brains interest you, and/or if you're a dog trainer looking for CEUs!]

About the Dog Zombie

Jessica Perry Hekman, DVM, PhD is fascinated by dog brains. She is a postdoctoral associate at the Broad Institute of MIT and Harvard, where she studies the genetics of dog behavior. Her interests include the stress response in mammals, canine behavior, canine domestication, shelter medicine, animal welfare, and open access publishing. You may learn more about Jessica at www.dogzombie.com, or email her at jph at dogzombie dot com. All opinions expressed here are her own.

For the animal shall not be measured by man… They are not brethren, they are not underlings: they are other nations, caught with ourselves in the net of life and time, fellow prisoners of the splendor and travail of the earth. (Henry Beston)